@deceptikon i have already mailed them twice and also message on fb (when i started this contest) but got no reply till now. but what amazed me is when i saw people submitted their solution in C and C++ and got points.
Try contacting the people who submitted solutions and ask what their approach was. Don't ask for the solution itself, just voice your concern about the ambiguity over N and ask how they got around it. My guess is that they made an unwarranted assumption that happened to be safe on the testing machine.